Pathogenesis of Nail Diseases PDF

Pathogenesis of nail diseases Outline Fungal infections of the nail Paronychia Systemic diseases affecting the nails Fungal infections of the nails Underlying mechanisms Definitions Nail dystrophy Any abnormality of the nail Onychomycosis Any fungal infection of the nails. Thi...

Pathogenesis of nail diseases Outline Fungal infections of the nail Paronychia Systemic diseases affecting the nails Fungal infections of the nails Underlying mechanisms Definitions Nail dystrophy Any abnormality of the nail Onychomycosis Any fungal infection of the nails. This includes dermatophyte and non-dermatophyte infections. Examples: Fusarium spp., Aspergillus spp., Candida spp. Tinea unguium Dermatophytic onychomycosis (i.e., dermatophyte infection of the nails) Accounts for about 90% of onychomycosis Examples: T. rubrum, T. interdigitale, T. tonsurans, and E. floccosum. Predisposing factors Local factors Chronic tinea pedis Chronic paronychia (→ candida spp) Trauma or other nail disorders Host factors Poorly controlled diabetes mellitus Immunosuppression e.g., HIV Peripheral vascular disease Environment Occlusive footwear Sweating  How do fungi enter the nail? How do fungi enter the nail? 1. distal/lateral subungual invasion via the hyponychium 2. superficial white direct penetration into the dorsal surface of the nail plate 3. proximal subungual invasion under the proximal nail fold (usually immunocompromised hosts) 4. mixed pattern ≥2 of the above patterns in the same nail Distal subungual Invasion via the hyponychium. Superficial white Direct penetration into the dorsal surface of the nail plate. Proximal subungual invasion under the proximal nail fold Immuno- compromised? How do fungi affect the nails? Subungual hyperkeratosis (keratin debris under the nail plate) Crumbling Thickening Discolouration Nail plate destruction Nail clippings and sub-ungual debris in the lab Fungal microscopy and culture Histology (or PCR, if available) Fungal hyphae on a formalin-fixed Periodic Acid Schiff (PAS) stained nail clipping. Send nail clippings in saline. Send nail clippings in formalin. References E. Wang, D. de Berker, A.M. Christiano Ch 68 Biology of the hair and nails. In Bolognia, Jean, L. et al. Dermatology. Available from: Elsevier eBooks, (4th Edition). 2017. B.E. Elewski, L.C. Hughey, K.M. Hunt, R.J. Hay. Ch 77 Fungal diseases. In Bolognia, Jean, L. et al. Dermatology. Available from: Elsevier eBooks, (4th Edition). 2017. James, William, D. et al. Ch 15 Diseases Resulting from Fungi and Yeasts. In Andrews' Diseases of the Skin. Available from: Elsevier eBooks, (13th Edition), 2019. A. Hillan. Fungal nail infections. Dermnet: all about the skin. October 2022. https://dermnetnz.org/topics/fungal-nail-infections Date accessed 23.05.2023 Paronychia Underlying mechanisms What is paronychia? Inflammation of the nailfold (usually proximal) Can be divided into acute and chronic forms Importance of the cuticle The cuticle (eponychium) acts as a seal to prevent irritants and pathogens entering beneath the proximal nailfold. Acute paronychia: mechanism Nail biting or sucking Manicures Port of entry for Minor trauma Ingrown toenails infections Medications e.g. oral retinoids Acute paronychia – which pathogens? Usually caused by bacterial infection Staphylococcus aureus or Streptococcus pyogenes Recurrent acute paronychia Herpes simplex virus (‘herpetic whitlow’) Chronic paronychia: mechanism Occupations that Irritants enter involve wet work, Disruption of (esp. H20) causing irritant contact cuticle inflammation at dermatitis of hands proximal nailfold Chronic paronychia and pathogens Chronic paronychia is caused by irritants (esp H20) and is not primarily an infection. However, secondary infections do occur, typically Candida (e.g., Candida albicans). References 1. E. Wang, D. de Berker, A.M. Christiano Ch 68 Biology of the hair and nails. In Bolognia, Jean, L. et al. Dermatology. Available from: Elsevier eBooks, (4th Edition). 2017. 2. B.E. Elewski, L.C. Hughey, K.M. Hunt, R.J. Hay. Ch 77 Fungal diseases. In Bolognia, Jean, L. et al. Dermatology. Available from: Elsevier eBooks, (4th Edition). 2017. 3. James, William, D. et al. Ch 15 Diseases Resulting from Fungi and Yeasts. In Andrews' Diseases of the Skin. Available from: Elsevier eBooks, (13th Edition), 2019. 4. A. Oakley, J. Gomez. Dermnet: paronychia. August 2017.. https://dermnetnz.org/topics/paronychia Date accessed 06.06.2023 Systemic diseases affecting the nails: an introduction Underlying mechanisms  Any abnormality of the Nail fingernail(s) and/or toenail(s) including abnormalities of: Shape dystrophy: Colour Texture definition Growth  Infections (see lecture on Nail fungal nail infections) Benign or malignant dystrophy: growths Cysts causes Systemic diseases